What happens if the EU signs off on the Brexit deal - and what happens if they don't

Theresa May (pictured at the Lord Mayor's Banquet on Monday) has struck a Brexit deal with Brussels - but now has to sell it to her Cabinet and then Parliament

Emergency EU Summit, Brussels, November 25

What will happen? The EU has scheduled a summit to sign off the Brexit deal covering the withdrawal and future trade - although there are fears that last minute wrangling over issues such as fishing rights and Gibraltar could derail the event altogether.

If it is cancelled the negotiating teams will keep working until they are in position to put an overall agreement to leaders - or they conclude the situation is hopeless.

The next routine EU summit is due to happen on December 13-14.

However, by that point time will be on the verge of running out - as both sides need to ratify the deal before March.

German Chancellor Angela Merkel (pictured) is still a crucial figure in the Brexit drama

The so-called 'meaningful vote' in the UK Parliament, December 2019

What will happen: Assuming a deal is reached, a debate, probably over more than one day, will be held in the House of Commons on terms of the deal.

It will end with a vote on whether or not MPs accept the deal. More than one vote might happen if MPs are allowed to table amendments.

The vote is only happening after MPs forced the Government to accept a 'meaningful vote' in Parliament on the terms of the deal.

What happens if May wins? If the meaningful vote is passed, there will be a series of further votes as the withdrawal treaty is written into British law.

It will be a huge political victory for the Prime Minister and probably secure her version of Brexit.

What happens if she loses? This is possibly the most dangerous stage of all.

The Prime Minister will have to stake her political credibility on winning a vote and losing it would be politically devastating.

Brexiteers do not want to sign off the divorce bill without a satisfactory trade deal and Remainers are reluctant to vote for a blind Brexit.

She could go back to Brussels to ask for new concessions before a second vote but many think she would have to resign quickly.

The Prime Minister (pictured at the EU Council in June) has made clear the UK will leave without a deal if MPs reject her package

Ratification in the EU, February 2019

What will happen? After the meaningful vote in the UK, the EU will have to ratify the agreement.

The European Parliament must also vote in favour of the deal. It has a representative in the talks, Guy Verhofstadt, who has repeatedly warned the deal must serve the EU's interests.

Will it be agreed? In practice, once the leaders of the 27 member states have agreed a deal, ratification on the EU side should be assured.

If the deal has passed the Commons and she is still in office, this should not be dangerous for the Prime Minister.

Exit day, March 29, 2019

At 11pm on March 29, 2019, Britain will cease to be a member of the European Union, two years after triggering Article 50 and almost three years after the referendum.

Exit happens at 11pm because it must happen on EU time.

If the transition deal is in place, little will change immediately - people will travel in the same way as today and goods will cross the border normally.

But Britain's MEPs will no longer sit in the European Parliament and British ministers will no longer take part in EU meetings.

Negotiations will continue to turn the political agreement on the future partnership into legal text that will eventually become a second treaty. Both sides will build new customs and immigration controls in line with what this says.

Transition ends, December 2020

The UK's position will undergo a more dramatic change at the end of December 2020, when the 'standstill' transition is due to finish.

If the negotiations on a future trade deal are complete, that could come into force.

But if they are still not complete the Irish border 'backstop' plan could be triggered.

Under current thinking, that means the UK staying in the EU customs union and more regulatory checks between mainland Britain and Northern Ireland.

Eurosceptics fear this arrangement will prevent the country striking trade deals elsewhere, and could effectively last for ever, as Brussels will have no incentive to negotiate a replacement deal.